The accessory gearbox, well known to a person skilled in the art under its abbreviation AGB, supports different auxiliary equipment mounted on the engine and necessary to its operation or to that of the aircraft. These various accessories can in particular comprise a generator, a starter, an alternator, hydraulic pumps for fuel or oil, and are driven mechanically by the engine shaft through transmission shaft. The necessary power for driving accessories is generally tapped mechanically from the compressor of the turbo machine.
Customarily, the AGB comprises gearing with parallel shafts so as to mechanically drive the accessories. The separation of the accessories is therefore determined by the distance between centers of the gearing and not by their respective sizes. To increase this separation it is therefore necessary to add one or more intermediate gears, which has the disadvantage of increasing both the size of the AGB and its mass. Moreover, the shafts of all the gearing of the AGB being parallel, the accessories necessarily have the same orientation with respect to the AGB and the engine.
Moreover, in the case of a turbofan engine, the gas generator is connected to a fan which is housed in a fan casing. The nacelle then has a generally circular section. The space available for accommodating the AGB is consequently defined by an annular portion housed in the nacelle, around the turbo machine, and consequently has a generally curved shape (see FIG. 1).
To improve engine performance, one solution consists of reducing the size of the nacelle at the fan so as to increase the size of the fan without thereby increasing the outer diameter of the turbo machine. The space available in the nacelle below the fan is therefore strongly reduced; it is therefore necessary either to reduce the size of the AGB so as to be able to be able to integrate it under the fan in the nacelle anyway, or to replace the AGB downstream of the fan in the central compartment of the turbo machine (that is in the “core” area), wherein the available space is even more limited.
Conventional turbofan AGBs are therefore not suitable from a structural, dimensional and function point of view to the new fan configurations and to the core area of the turbo machine.
An AGB has therefore been proposed in document FR 1355241 in the name of the applicant comprising:
a primary angle drive formed from an input gear wheeling member driven by the engine shaft of the turbofan and from a primary gearing member,
at least one mechanical drive assembly of the accessory transmission shaft, which is driven by the primary drive means through a secondary angle drive comprising two meshing non-parallel gearing members.
Such an AGB with gearing with non-parallel axes has the advantage of being easily modulated and to also allow flexibility in installing different accessories by not having to consider their size, without however modifying their drive speed.
However, updating of specifications on an AGB can lead to changes in accessories or in rotation speeds on certain existing lines, which involves redefining the kinematic chain of the AGB and the risk increases arising therefrom.